A Useful coffeescript "defaults" function , which even does type checking.

apply_defaults.coffee

applyDefaults = (source, defaults) ->
  ###
  # Recursively applies defaults to the source object
  ###
  #The Mandatory safety checks
  return source  if not source?
  return defaults if not defaults?
  #First fill the results with defaults of each proprerty, recursively
  result = {}
  for prop of defaults
    if not source[prop]? or typeof (defaults[prop]) isnt typeof (source[prop])
      result[prop] = defaults[prop]
    #Another check as Javascript Arrays are just javascript objects with integer keys
    else if typeof (defaults[prop]) is "object" and not _.isArray defaults[prop]
      result[prop] = applyDefaults(source[prop], defaults[prop])

  #Then Fill in the holes of defaults with the values from source
  for prop of source
    result[prop] = source[prop]  unless result[prop]?
  return result